1. Field of the Invention
The present invention relates to wear protectors and in particular, though not exclusively, to a method and apparatus for the application of a sleeve upon a tubular, such as a pipe string, used in downhole applications, for example in oil and gas exploration or recovery.
2. Description of Related Art
In oil and gas exploration and recovery procedures involving movement of a pipe string within a well bore contact normally occurs between the pipe string and the well bore or between the pipe string and an external casing already present in the well bore. Such contact can cause wear or perhaps even damage to the outer surface of the pipe string and the casing.
Conventionally the problem of wear upon the pipe string has been addressed by the provision of wear protection at strategic points on its outer surface, for example, at joints. Such wear protection is positioned on the outer surface of the pipe string to at least reduce contact between the outer surface of the pipe string and the wellbore, thereby reducing wear of the outer surface of the pipe string.
Conventional wear protection typically takes the form of strips of a hardwearing metal composition, such as nickel based tungsten carbide. Alternatively, the wear protection may be provided in the form of a coating of such a material over the entire outer surface of at least part of the length of the pipe string (i.e. wear banding). Pads of material may also be arranged on the surface of the pipe string. Clearly the wear protection is subject to wear when in use that would otherwise be sustained by the pipe string itself. Thus, in time the wear protection itself needs repair or replacement.
Repair or replacement of wear protection typically involves welding, and the present applicants have recognised the significance of applying heat to a pipe string during the welding process. More specifically, the structural integrity of the pipe string can be compromised by the application of heat. Thus, the pipe string is normally inspected when welding is complete to determine whether or not any structural weakness has arisen. Whatever structural weakness there is may then need to be remedied by an appropriate treatment, such as annealing. The present applicants have appreciated that such processes require specialist equipment and personnel that may only be available far from the site of use of the pipe string. Moreover, such processes are of themselves normally burdensome in cost and time.
A further type of wear protector is formed by providing the band of material as a separate sleeve located around the pipe string or tubular. These sleeves can be fixed to rotate with the tubular, often termed ‘rotating’ type, or may rotate relative to the tubular, termed ‘non-rotating’ type. Non-rotating sleeves are required to be axially retained on the tubular between raised ends or stops. This provides a disadvantage for assembly. Either the tubing must contain a threaded joint between the stops to allow the tubular to be separated to insert the sleeve, or the sleeve must be of component parts which connect together to provide an annular band. It is recognised in the industry that any joint or connection provides a potential weak point which may be prone to failure.
An object of the present invention is therefore to provide a method of applying a sleeve to a tubular which mitigates at least some of the disadvantages of the prior art.
A further object of the present invention is to provide a sub including a sleeve which is adapted for use as a wear protector.
According to a first aspect of the present invention there is provided a method of creating a sleeve on tubing for use in a well bore, the method comprising the steps:    (a) locating a mould around the tubular, the mould comprising at least first and second portions, the portions including opposite mating surfaces to engage adjacent portions such that a seal is provided between the portions and the mould including first and second ends, the ends being arranged to provide a seal against the tubular when the mould is located around the tubular with the portions providing at least one circumferential recess in the mould;    (b) inserting a composite material into the/each recess through at least one entry port in the mould;    (c) curing the composite material; and    (d) removing the mould to there provide a composite sleeve around the tubular.
In this way there is no requirement to break the tubular to insert the sleeve and the sleeve is of single piece construction. Additionally the use of a composite material, which is cured, removes the need to heat the tubular to temperatures which could affect the integrity of the tubular. Indeed, the simplicity of the system makes it readily available for use at the well head. The sleeve provides a wear protector upon the tubular.
Preferably, the method includes the step of keying at least a portion of the surface of the tubular prior to step (a). Keying the tubular may be done by sand blasting or another roughing method which provides better adhesion of the composite material to the tubular.
Optionally, the method includes the step of coating at least a portion of the tubular with a stand-off material prior to step (a). Preferably, the method includes the step of removing the stand-off material once the composite material has cured. By using a stand-off material such as wax, adhesion of the composite material is prevented and a clearance is created between the tubular and the sleeve so that the sleeve may rotate relative to the tubular.
Preferably, the method includes the steps of keying circumferential bands on either side of a central band longitudinally arranged on the tubular. This provides a central non-rotating sleeve bounded by end stops in-situ.
Advantageously, the method includes the step of inserting the composite material into at least one further recess arranged on the circumferential recess of the mould, the at least one further recess being arranged as a pad. This allows pads to be incorporated during manufacture of the sleeve. Such wear pads provide wear protection while also allowing fluid to easily bypass the sleeve in the well bore. Alternatively a wear pad may be made in the further recess and then applied to the sleeve as the sleeve is moulded. The pad may be made of a composite material. Here the composite sleeve will attach the pad to the tubular.
It should be noted that these wear pads are not blades or fins as would be found on centralisers. Any centralising ability of the pads would be quickly lost due to the uneven wear to which the pads are exposed to. The material of the pads is also selected to be sacrificial to advantageously reduce friction between the string and casing, this is not the case for blades on centralisers. The use of pads and the shape selected for them is chosen to allow optimum fluid flow past the wear protector sleeve in use.
Preferably the step of curing the composite material is achieved by leaving the mould upon the tubular for a period of time at ambient temperature. Thus the method can be carried out at any location, i.e. at the well head or platform. Additional heating may be applied to the composite material prior to insertion in the mould. In this way the viscosity of the material can be decreased to aid insertion to the mould. This pre-heating temperature may be up to approximately 50 degrees C.
Following curing, heat may optionally be applied to the sleeve to enhance advantageous properties of the composite material. Such properties may include increased wear resistance, heat resistance etc. This heating effectively gives the material a ‘memory’ quality. Such heating may be to temperatures up to approximately 150 degrees C. These temperatures are still below approximately 600-800 degrees C., these being the minimum temperature where the structural integrity of the metal tubular may need to be considered.
Preferably also, the method may include the step of inserting a matrix material in at least one recess. The matrix may be a webbing of high strength material to which the composite adheres. This will improve the tensile strength of the sleeve. Alternatively, the method may include the step of wrapping a bandage of material around the tubular prior to locating the mould on the tubular over the bandage. The bandage may be a webbing soaked in a composite or glass fibre mix and applied before it sets or cures. Again this will improve the strength of the sleeve.
Preferably, the composite material comprises at least two composite components, which when mixed are in a mouldable condition and which subsequently change to a rigid condition. More specifically, one of the composite components may comprise a catalyst. Additionally, the composite material may be a sacrificial material. In this way, the sacrificial material will wear away upon contact to and in preference to the surface of the well bore or casing bore.
According to a second aspect of the present invention there is provided a sub for location in a tubular string within a well bore, the sub comprising a tubular body having first and second ends adapted for connection in a tubular string; a continuous single piece sleeve located around the tubular body, the sleeve arranged to move axially and rotationally upon the tubular body; first and second end stops, the stops comprising continuous single piece annular bands located around the body at either side of the sleeve, the stops being fixed upon the body such that they limit the axial movement of the sleeve and wherein the sleeve and stops all comprise a composite material.
Preferably the sub is a wear protector.
Preferably the sub is formed by a method according to the first aspect. In this way the composite material may be identical for the sleeve and the stops. The sleeve may further comprise a matrix in the form of a web imbedded within the composite material. Alternatively, or additionally, the sleeve may further comprise a bandage arranged circumferentially within the composite material.
Advantageously there may be arranged on the sleeve one or more wear pads, the pads comprising the composite material.
Preferably the sleeve has an outer diameter greater than an outer diameter of the stops.
According to a third aspect of the present invention there is provided a mould for use in providing a sleeve by a method according to the first aspect, the mould comprising at least first and second portions, the portions including opposite mating surfaces to engage adjacent portions such that a seal is provided between the portions and the mould including first and second ends, the ends being arranged to each provide a circumferential seal against a tubular when the mould is located around a tubular with the portions providing at least one circumferential recess in the mould. The mould can thus be located around the tubular and a material injected into the mould, left to set and the mould removed.
Preferably, there are arranged two circumferential indents spaced apart longitudinally on the mould, each indent traversing the portions and having a depth approximately equal to a depth of the recess at the location of the indent. In this way, a sleeve with integral stops can be provided.